Synopsis: Published: 2015-06-15 (Rev. 2017-02-20) - List of low and high mercury concentration levels in fish, includes chart of fish species safe and not safe for pregnant women and the public to eat. For further information pertaining to this article contact: Ian Langtree at Disabled World.

Definition: Mercury

Mercury is defined as a chemical element with symbol Hg and atomic number 80. It is commonly known as quicksilver and was formerly named hydrargyrum. Mercury occurs in deposits throughout the world mostly as cinnabar (mercuric sulfide). Mercury can be absorbed through the skin and mucous membranes and mercury vapors can be inhaled, so containers of mercury are securely sealed to avoid spills and evaporation. The most toxic forms of mercury are its organic compounds, such as dimethylmercury and methylmercury. Mercury can cause both chronic and acute poisoning.

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"Mercury is known to bio-accumulate in humans, so bio-accumulation in seafood carries over into human populations, where it can result in mercury poisoning."

The U.S. FDA recommends eating 8 - 12 ounces of fish low in mercury per week. Fish contain vital nutrients including omega 3 fatty acids, protein, vitamins, and minerals such as iron. These nutrients are essential, particularly for pregnant moms, as they foster healthy fetal, infant, and childhood development. However, some types of fish contain a lot higher mercury levels than others.

Mercury poisoning (also known as hydrargyria or mercurialism) is a type of metal poisoning and a medical condition caused by exposure to mercury or its compounds. Symptoms typically include sensory impairment (vision, hearing, speech), disturbed sensation and a lack of coordination. The type and degree of symptoms exhibited depend upon the individual toxin, the dose, and the method and duration of exposure.

US government scientists tested fish in 291 streams around the country for mercury contamination. They found mercury in every fish tested, according to the study by the U.S. Department of the Interior. They found mercury even in fish of isolated rural waterways. 25% of the fish tested had mercury levels above the safety levels determined by the U.S. Environmental Protection Agency for people who eat the fish regularly.

Mercury-containing plants and tiny animals are eaten by smaller fish that are then eaten by larger fish, whose tissue accumulates mercury. That is why larger, longer-living predators such as sharks and swordfish tend to have more of the toxin than smaller fish such as sardines, sole, and trout.

Fish and shellfish concentrate mercury in their bodies, often in the form of methylmercury, a highly toxic organic compound of mercury. Mercury is known to bio-accumulate in humans, so bio-accumulation in seafood carries over into human populations, where it can result in mercury poisoning. The presence of mercury in fish can be a particular health concern for women who are or may become pregnant, nursing mothers, and young children.

Mercury levels in the northern Pacific Ocean have risen about 30 percent over the past 20 years and are expected to rise by 50 percent more by 2050 as industrial mercury emissions increase, according to a 2009 study led by researchers at the U.S. Geological Survey and Harvard University. When you eat seafood containing methylmercury, more than 95 percent is absorbed, passing into your bloodstream. It can move throughout your body, where it can penetrate cells in any tissue or organ.

In comments submitted to federal health officials, a group of scientists and policy analysts pointed out that a 6-ounce serving of salmon contains about 4 micrograms of mercury vs. 60 micrograms for the same portion of canned albacore tuna - and 170 micrograms for swordfish.

The list below shows the amount of various types of fish that a woman who is pregnant or planning to become pregnant can safely eat, according to the Environmental Protection Agency (EPA).